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Aplasia cutis congenita
Aplasia cutis congenita (ACC) is a rare skin disorder characterized by localized absence of skin that is usually located on the scalp but can occur anywhere on the body including the face, trunk and extremities. ACC may occasionally be associated with other anomalies.
Incidence is approximately 1/10,000 births.
ACC is noticed immediately at birth and usually presents as a solitary lesion on or near the vertex. There may also be multiple lesions occurring on the scalp or elsewhere. The individual lesion can vary from a superficial, circular or oval, well-demarcated atrophic scar with alopecia to a weeping or granulating ulcer extending to the bone. The lesions can range from few millimeters to more than 10 cm in diameter. Some defects can have a membranous covering that can be filled with fluid, giving it a bullous appearance. A tuft of long, dark colored hair (hair collar sign) is often found around the membranous lesion suggesting cranial dysraphism. Membranous ACC is not associated with non-neurectodermal anomalies.
Etiology is manifold; genetic factors, teratogens, amniotic adhesion, vascular anomalies, pharmacological agents (e.g. methimazole, benzodiazepines), intrauterine trauma and infections have all been implicated. Membranous ACC of the scalp has been proposed to be due to incomplete closure of ectodermal fusion lines. A mutation in the GTPaseBMS1 (10q11.21) that reduces cell proliferation, recently has been linked to the disease.
Newborns with ACC have to be thoroughly examined for associated anomalies. Extensive cases of ACC necessitate immediate MRI to evaluate any accompanying bone and intracranial malformations. Histologic examination of ACC shows scar-like tissue devoid of skin appendages and elastic fibres. Membranous ACC may reveal heterotopic brain tissue.
Differential diagnoses include localized scalp infection, congenital dermoid cyst, small meningocoele, nodular neuronal heterotopia (see this term) and traumatic lesions. As the child grows and scarring occurs, didymosis aplasticosebacea, localized scleroderma (see these terms), sebaceous nevus and nevus psiloliparus should be considered. In extensive ACC, inherited epidermolysis bullosa and lethal restrictive dermopathy (see these terms) are differential diagnoses. ACC can occur as part of syndromes including: chromosomal abnormalities (mainly trisomy 13), Adams-Oliver, Johanson-Blizzard, Anklyoblepharon-ecodermal defects-cleftlip/plate syndrome, EEC syndromes, SCALP syndrome, focal facial dermal dysplasia type IV, oculocerebrocutaneous syndrome, microphthalmia with linear skin defects syndrome, Toriello-Lacassie-Droste syndromes, Aplasia cutis congenita - intestinal lymphangiectasia, Aplasia cutis - myopia, and cutis verticis gyrata - thyroid aplasia - intellectual disability (see these terms).
Most reported cases are sporadic, but autosomal dominant inheritance has been reported in familial cases.
Management and treatment
Biopsy, drainage or excision of lesions should not be undertaken without prior imaging. Treatment of ACC usually involves a conservative approach (gentle cleansing, topical antiseptics, hydrocolloidal dressings) allowing the lesions to heal by secondary intention when possible. Repair using skin flaps and grafts is only recommended for larger defects, such as those extending down to the dura mater, to prevent any hemorrhage and infection.
Less severe cases usually resolve within weeks to months, but alopecia persists. Underlying or associated defects may significantly affect mortality and morbidity.